A telephone subscriber engaged in an ongoing conversation with a second party may place a new call to a third party while placing the call with the second party on hold.
A so-called "call hold" service, one of supplementary services provided by a telephone operating company, has conventionally accommodated the above-mentioned service feature. The call hold service has been typically implemented in and provided by a switching system at a central office.
In recent years, meanwhile, the popularity of wireless communications has grown immensely and the growth is expected to continue further in the future. Known as a rather efficient wireless communications system is a CDMA(Code Division Multiple Access) communications system.
Referring to FIG. 1, there is shown a simplified structure of a CDMA communications system. The CDMA communications system interfaces to a Public Switched Telephone Network(PSTN) 14 on one side and to a mobile station(MS) 10 on the other side. The CDMA communications system is comprised of four major elements: the MS 10, a base station(BS) 11, a base station controller(BSC) 12, and a mobile switching system(MSS) 13.
The MS 10, a so-called cellular phone, a terminal equipment, provides communication access for cellular users to communicate with each other or with PSTN users.
The BS 11 is a link between the MS 10 and the BSC 12 and provides a common air interface to the MS 10.
The BSC 12 contains resources providing a channel between the BS 11 and the MSS 13. The BSC 12 performs functions such as: providing communication gateway between different BSs; processing and reformatting the data from the BS 11 to the MSS 13, and vice versa; and controlling call processing and signalling with the MSS 13.
The MSS 13 is a link between the BSC 12 and the PSTN 14. The MSS 13 provides switching functions required to properly pass data between the BSC 12 and PSTN 14. The MSS 13 may also include other functions or systems, including but not limited to, the operation and management, a home location register, a visitor location register, and an authentication center.
On the other hand, it is commonplace that a wireless customer demands the supplementary services such as a call hold service.
The MSS 13 is required to provide various supplementary services such as the call hold service as a conventional switching system has provided with.
There has been provided a procedure for handling the call hold service for conventional telephone subscriber by the conventional switching system. However, there has not been provided a call hold procedure applicable for the mobile switching system employed in the CDMA communications system.